Polishing composition, polishing method, and method of producing semiconductor substrate

ABSTRACT

A polishing composition according to the present invention contains abrasive grains, a basic inorganic compound, an anionic water-soluble polymer, and a dispersing medium, in which a zeta potential of the abrasive grains is negative, an aspect ratio of the abrasive grains is 1.1 or less, in a particle size distribution of the abrasive grains obtained by a laser diffraction/scattering method, a ratio D90/D50 of a particle diameter D90 when an integrated particle mass reaches 90% of a total particle mass from a fine particle side to a particle diameter D50 when the integrated particle mass reaches 50% of the total particle mass from the fine particle side is more than 1.3, and the basic inorganic compound is an alkali metal salt.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based on Japanese Patent Application No.2020-049621 filed on Mar. 19, 2020, and a disclosed content thereof isincorporated herein as a whole by reference.

BACKGROUND 1. Technical Field

The present invention relates to a polishing composition, a polishingmethod, and a method of producing a semiconductor substrate.

2. Description of Related Arts

In recent years, a so-called chemical mechanical polishing (CMP)technique for physically polishing and flattening a semiconductorsubstrate in producing a device has been used in accordance withmultilayer wiring on a surface of a semiconductor substrate. The CMP isa method for flattening a surface of an object to be polished (targetobject) such as a semiconductor substrate by using a polishingcomposition (slurry) containing abrasive grains such as silica, alumina,or ceria, an anti-corrosion agent, a surfactant, or the like.Specifically, it is used in processes such as shallow trench isolation(STI), flattening of an interlayer dielectric film (ILD film), tungstenplug formation, and formation of a multilayer wiring composed of copperand a low dielectric constant film.

For example, JP 2001-185516 A discloses a polishing compositioncontaining a water-soluble polymer to which alkylene oxide is added,polyacrylic acid, and abrasive grains. According to this technique, itis possible to polish at a high polishing speed and suppress theoccurrence of scratches on the polished surface of the object to bepolished due to polishing.

SUMMARY

However, it has been found that the technique disclosed in JP2001-185516 A has a problem in that the improvement of the polishingspeed is still insufficient.

Therefore, an object of the present invention is to provide a polishingcomposition capable of polishing an object to be polished at a highpolishing speed.

The present inventor has made extensive studies in order to solve theabove problems. As a result, it has been found that the above-mentionedproblem can be solved by a polishing composition containing abrasivegrains, a basic inorganic compound, an anionic water-soluble polymer,and a dispersing medium, in which a zeta potential of the abrasivegrains is negative, an aspect ratio of the abrasive grains is 1.1 orless, in a particle size distribution of the abrasive grains obtained bya laser diffraction/scattering method, a ratio D90/D50 of a particlediameter D90 when an integrated particle mass reaches 90% of a totalparticle mass from a fine particle side to a particle diameter D50 whenthe integrated particle mass reaches 50% of the total particle mass fromthe fine particle side is more than 1.3, and the basic inorganiccompound is an alkali metal salt.

DETAILED DESCRIPTION

Hereinafter, embodiments of the present invention will be described;however, the present invention is not limited to the followingembodiments. Unless otherwise specified, measurements of operations,physical properties, and the like are performed under the conditions ofroom temperature (20° C. to 25° C.)/relative humidity 40 to 50% RH.Further, in the present specification, “X to Y” indicating a range means“X or more and Y or less”.

<Polishing Composition>

The present invention relates to a polishing composition used forpolishing an object to be polished, the polishing composition containsabrasive grains, a basic inorganic compound, an anionic water-solublepolymer, and a dispersing medium, in which a zeta potential of theabrasive grains is negative, an aspect ratio of the abrasive grains is1.1 or less, in a particle size distribution of the abrasive grainsobtained by a laser diffraction/scattering method, a ratio D90/D50 of aparticle diameter D90 when an integrated particle mass reaches 90% of atotal particle mass from a fine particle side to a particle diameter D50when the integrated particle mass reaches 50% of the total particle massfrom the fine particle side is more than 1.3, and the basic inorganiccompound is an alkali metal salt.

The reason why the polishing composition of the present invention exertsthe above effect is not always clear, but it is considered as follows.

The polishing composition generally polishes an object to be polished bya physical action of rubbing a surface of a substrate, a chemical actionof components other than abrasive grains on the surface of thesubstrate, and a combination thereof. As a result, the form and type ofthe abrasive grains have a great influence on the polishing speed.

The polishing composition of the present invention contains abrasivegrains having a predetermined shape and a predetermined particle sizedistribution. That is, the abrasive grains used in the polishingcomposition are composed of spherical particles that are close to a truesphere because the aspect ratio is 1.1 or less, and further are composedof particles having a wide particle size distribution when D90/D50 ismore than 1.3. Since the abrasive grains are the spherical particlesthat are close to a true sphere, the abrasive grains roll efficiently ona surface to be polished. As a result, the abrasive grains cansufficiently apply a mechanical force to the polished surface whilerolling, and can appropriately polish the surface to be polished.Further, since the particle size distribution of the abrasive grains iswide, there are relatively small-sized abrasive grains and relativelylarge-sized abrasive grains. The abrasive grains having a relativelysmall size are prevented from rolling on the surface to be polished bycoming into contact with the abrasive grains having a relatively largesize, and tend to stay on the surface to be polished. When therelatively small size particles staying on the surface to be polishedstart rolling again due to contact with other particles or the like, alarge mechanical force is applied to the surface to be polished for theparticle size. As described above, it is presumed that the abrasivegrains in which spherical particles that are close to a true sphere havea wide particle size distribution can realize effective polishing ateach particle size, and can further increase the polishing speed of theobject to be polished. That is, the present invention has found abalance between the aspect ratio of the abrasive grains and the particlesize distribution that can effectively act on the surface to bepolished.

Further, the abrasive grains contained in the polishing composition ofthe present invention have a negative zeta (0 potential. In other words,the abrasive grains having a negative zeta potential are used in thepolishing composition. Here, since the anionic water-soluble polymercontained in the polishing composition of the present invention is apolymer, it easily adheres to the surface of a polishing pad (forexample, polyurethane). The zeta potential on the surface of thepolishing pad becomes negative due to the adhesion of the anionicwater-soluble polymer to the surface of the polishing pad. Specifically,in a case where the zeta potential on the pad surface is positive, thezeta potential on the pad surface becomes negative due to the adhesionof the anionic water-soluble polymer, and in a case where the zetapotential on the pad surface is negative, the adhesion of anionicwater-soluble polymer increases the absolute value of the zeta potentialthereof. Therefore, when the polishing composition is used to polish theobject to be polished, it is presumed that a repulsive force due tonegative charges is generated between the polishing pad in contact withthe polishing composition and the abrasive grains in the polishingcomposition, and this repulsion makes it easier for the abrasive grainsto act on the surface of the object to be polished, thereby furtherimproving the polishing speed.

Further, the polishing composition of the present invention contains abasic inorganic compound which is an alkali metal salt. For example, abasic inorganic compound tends to increase the electrical conductivityof a polishing composition as compared with the basic organic compound.It is considered that this further improves the polishing speed by thepolishing composition. Further, since the basic inorganic compound is analkali metal salt, it does not have a three-dimensional bulkiness ascompared with the basic organic compound, and thereby, the basicinorganic compound and the anionic water-soluble polymer are less likelyto form an aggregate. Therefore, in the polishing composition of thepresent invention, since the anionic water-soluble polymer is in astable dispersed state, the anionic water-soluble polymer can beefficiently adhered to the polishing pad.

As described above, it is considered that the polishing composition ofthe present invention has further improved polishing characteristics ofthe abrasive grains by containing the abrasive grains having apredetermined shape and a predetermined particle size distribution andhaving high polishing power in combination with an anionic water-solublepolymer and a specific basic inorganic compound. However, it goeswithout saying that such a mechanism is merely presumption and does notlimit the technical scope of the present invention.

[Object to be Polished]

The material contained in the object to be polished by the polishingcomposition of the present invention is not particularly limited, andexamples thereof include silicon oxide, silicon nitride (SiN), siliconcarbonitride (SiCN), polycrystalline silicon (polysilicon), amorphoussilicon, metal, SiGe, and the like.

The object to be polished according to the present invention preferablycontains silicon oxide or silicon nitride, and more preferably containssilicon oxide. Therefore, the polishing composition of the presentinvention is preferably used for polishing an object to be polishedcontaining silicon oxide or silicon nitride, and more preferably usedfor polishing an object to be polished containing silicon oxide.

Examples of films containing silicon oxide include a TEOS (TetraethylOrthosilicate) type silicon oxide film (hereinafter, also simplyreferred to as “TEOS film”) produced by using tetraethyl orthosilicateas a precursor, and a HDP (High Density Plasma) film, an USG (UndopedSilicate Glass) film, a PSG (Phosphorus Silicate Glass) film, a BPSG(Boron-Phospho Silicate Glass) film, an RTO (Rapid Thermal Oxidation)film, and the like.

[Abrasive Grain]

The polishing composition of the present invention contains abrasivegrains. The type of the abrasive grains used in the polishingcomposition of the present invention is not particularly limited, andexamples thereof include oxides such as silica, alumina, zirconia, andtitania. The abrasive grains may be used either singly or in combinationof two or more types. As the abrasive grains, a commercially availableproduct or a synthetic product may be used. The type of the abrasivegrains is preferably alumina. That is, the polishing composition of thepresent invention contains alumina (preferably alumina obtained by avaporized metal combustion method described later) as the abrasivegrains.

In the polishing composition of the present invention, the abrasivegrains exhibit a negative zeta potential, an aspect ratio of theabrasive grains is 1.1 or less, in a particle size distribution of theabrasive grains obtained by a laser diffraction/scattering method, aratio D90/D50 of a particle diameter D90 when an integrated particlemass reaches 90% of a total particle mass from the fine particle side toa particle diameter D50 when the integrated particle mass reaches 50% ofthe total particle mass from the fine particle side is more than 1.3.

The abrasive grain used for the polishing composition of the presentinvention exhibits a negative zeta potential. Here, the “zeta (0potential” is a potential difference that occurs at the interfacebetween a solid and a liquid that are in contact with each other whenthey perform relative motion. In the polishing composition of thepresent invention, the polishing speed of the object to be polished canbe improved by having the abrasive grains with a negative charge. Thezeta potential of the abrasive grains is preferably −80 mV or more and−5 mV or less, and more preferably −60 mV or more and −20 mV or less.When the abrasive grains (alumina) have a zeta potential in such arange, the polishing speed for the object to be polished can be furtherimproved.

The zeta potential of the abrasive grain in the polishing composition iscalculated by putting the polishing composition in ELS-Z2 manufacturedby Otsuka Electronics Co., Ltd., to perform a measurement at temperature25° C. using a flow cell by a laser Doppler method (electrophoreticlight scattering measurement method), and then analyzing the obtaineddata by a Smoluchowski equation.

The aspect ratio of the abrasive grains used in the polishingcomposition of the present invention is 1.1 or less. By using theabrasive grains having an aspect ratio of 1.1 or less, the abrasivegrains roll effectively on the surface to be polished, which improvesthe polishing speed. In the polishing composition of the presentinvention, when the aspect ratio of the abrasive grains is more than1.1, many abrasive grains may stay on the surface to be polished, andmany remaining abrasive grains may cause overpolishing. The aspect ratioof the abrasive grains is preferably less than 1.1, more preferably 1.09or less, and still more preferably 1.08 or less. Within such a range,the polishing speed can be more improved. It is presumed that sphericalparticles that are close to a true sphere are less likely to be deformedor broken due to deformation when stress is applied, and can transmitlarger stress to the object to be polished. Since the aspect ratio ofthe abrasive grains is 1 in a case of the true sphere, the lower limitthereof is 1 or more. The aspect ratio of the abrasive grains is anaverage value obtained by taking the smallest rectangle circumscribingthe image of an abrasive particle with a scanning electron microscopeand dividing the length of a long side of the rectangle by the length ofa short side of the same rectangle, and can be determined using generalimage analysis software. Specifically, the aspect ratio is calculatedfrom an equation “average major axis/average minor axis” after byrandomly selecting 100 abrasive grains from the images measured by ascanning electron microscope (SEM) (product name: SU8000 manufactured byHitachi High-Technology Co., Ltd.) and measuring and calculating theiraverage major axis and average minor axis. Details of the method formeasuring and calculating the aspect ratio of the abrasive grains willbe described in examples.

In the abrasive grains used in the polishing composition of the presentinvention, in a particle size distribution obtained by a laserdiffraction/scattering method, a ratio D90/D50 of a particle diameterD90 when an integrated particle mass reaches 90% of a total particlemass from the fine particle side to a particle diameter D50 when theintegrated particle mass reaches 50% of the total particle mass from thefine particle side is more than 1.3. As a result, in the polishingcomposition, there are relatively small-sized abrasive grains andrelatively large-sized abrasive grains. The abrasive grains having arelatively small size are prevented from rolling on the surface to bepolished by coming into contact with the abrasive grains having arelatively large size. As a result, the relatively small size of theabrasive grains can sufficiently apply a mechanical force to the objectto be polished during the polishing, and the polishing speed of theobject to be polished can be further improved. In a case where theD90/D50 is 5.0 or less, the polishing speed will decrease.

D90/D50 is preferably 1.5 or more, more preferably 1.8 or more, stillmore preferably 2.0 or more, and particularly preferably 2.5 or more.Within such a range, the polishing speed can be more improved. In theparticle size distribution of the abrasive grain in the polishingcomposition, which is obtained by the laser diffraction scatteringmethod, the upper limit of D90/D50 which is a ratio of a particlediameter (D90) when the integrated particle mass reaches 90% of thetotal particle mass from the fine particle side to a particle diameter(D50) when the integrated particle mass reaches 50% of the totalparticle mass from the fine particle side is not particularly limited,and it is preferably 4.0 or less, and is more preferably 3.5 or less.Within such a range, defects such as scratches, which may be generated,can be suppressed on the surface of the object to be polished afterpolishing using the polishing composition.

A size of the abrasive grain is not particularly limited, but a lowerlimit of an average primary particle size of the abrasive grainsobtained by image analysis from the observation photograph of thescanning electron microscope is preferably 10 nm or more, morepreferably 25 nm or more, and still more preferably 50 nm or more. Inaddition, in the polishing composition of the present invention, theupper limit of the average primary particle size of the abrasive grainsis preferably 500 nm or less, more preferably 250 nm or less, and stillmore preferably 200 nm or less. Within such a range, defects such asscratches, which may be generated, can be suppressed on the surface ofthe object to be polished after polishing using the polishingcomposition. That is, the average primary particle size of abrasivegrains is preferably 10 nm or more and 500 nm or less, more preferably25 nm or more and 250 nm or less, and further preferably 50 nm or moreand 200 nm or less. The average primary particle size of the abrasivegrains is calculated based on, for example, the specific surface area ofthe abrasive grain measured by a BET method.

In the polishing composition of the present invention, the lower limitof an average secondary particle size of the abrasive grains ispreferably 30 nm or more, more preferably 80 nm or more, still morepreferably 100 nm or more, and even more preferably 150 nm or more. Inaddition, in the polishing composition of the present invention, theupper limit of the average secondary particle size of the abrasivegrains is preferably 1000 nm or less, more preferably 500 nm or less,still more preferably 400 nm or less, and particularly preferably 350 nmor less. Within such a range, defects such as scratches, which may begenerated, can be suppressed on the surface of the object to be polishedafter polishing using the polishing composition. That is, the averagesecondary particle size of abrasive grains is preferably 30 nm or moreand 1000 nm or less, more preferably 80 nm or more and 500 nm or less,still more preferably 100 nm or more and 400 nm or less, andparticularly preferably 150 nm or more and 350 nm or less. Note that,the average secondary particle size of the abrasive grains can bemeasured, for example, by a dynamic light scattering method representedby a laser diffraction scattering method. That is, the average secondaryparticle size of the abrasive grains corresponds to the particlediameter D50 when the integrated particle mass reaches 50% of the totalparticle mass from the fine particle side, in a particle sizedistribution of the abrasive grains obtained by a laserdiffraction/scattering method.

An average association degree of the abrasive grains is preferably 4.0or lower, more preferably 3.0 or lower, and still more preferably 2.5 orlower. As the average association degree of the abrasive grains isdecreased, the generation of defects on the surface of the object to bepolished can be further reduced. In addition, the average associationdegree of the abrasive grains is preferably 1.5 or higher, and is morepreferably 1.8 or higher. As the average association degree of theabrasive grains is increased, there is an advantage in that thepolishing speed by the polishing composition is improved. Note that, theaverage association degree of the abrasive grains can be obtained bydividing the value of the average secondary particle size of theabrasive grains by the value of the average primary particle size.

The size of the abrasive grain (average particle size, aspect ratio,D90/D50, and the like) can be appropriately controlled by the selectionand the like of the method for producing the abrasive grains.

The abrasive grains used in the present invention preferably have afracture strength of 0.5 GPa or more. The fracture strength of theabrasive grains is not particularly limited as long as it is 0.5 GPa ormore, and is preferably 0.6 GPa or more, more preferably 0.65 GPa ormore, still more preferably 0.7 GPa or more, even more preferably 0.75GPa or more, and is particularly preferably 0.8 Pa or more. Within theabove range, the polishing speed is further improved. The fracturestrength of alumina is preferably 2 GPa or less. Within the above range,the production suitability is further improved while maintaining a highpolishing speed.

The fracture strength of the abrasive grains can be calculated withreference to “Rapid Determination of the Tensile Strength of Rocks withIrregular Test Pieces, HIRAMATSU Yoshio, OKA Yukitoshi, KIYAMA Hideo,Journal of the Mining and Metallurgical Institute of Japan, Vol. 81, No.932, 1024-1030, 1965”. Specifically, when particles (particularlyspherical particles) are compressed, compressive stress is distributednear a loading point, but tensile stress is distributed almost all overthe other parts. Therefore, the fracture strength of alumina can becalculated according to the following equation by recording the obtainedload-push displacement diagram and assuming that the point where thedisplacement increases rapidly is a point where large-scale fractureoccurs in the particles.

S _(t)=(2.8×P)/(π×d ²)  [Equation 1]

in the equation,S_(t) represents a fracture strength [GPa],P represents a fracture load [kgf], andd represents an average particle size [μm] of particles.

Here, a fracture load P can be measured using a microcompression testerMCTW-500 manufactured by Shimadzu Corporation and a flat surfaceindenter made of diamond (φ=50 μm). Further, the method for measuring anaverage particle size d will be described later in the description ofthe average particle size. Details of the method for measuring andcalculating the fracture strength of alumina will be described inexamples.

Note that, the fracture strength of the abrasive grains calculated basedon the above measurement is the same value even if the measurement isperformed in a state of a raw material (for example, powdered alumina)of the polishing composition or the abrasive grains (for example,alumina) are taken out from the prepared polishing composition andmeasured.

When alumina is used as the abrasive grains, it can be appropriatelyselected from various known alumina to be used. Examples of knownalumina include alumina containing at least one selected from α-alumina,γ-alumina, δ-alumina, θ-alumina, η-alumina, and κ-alumina, for example.Further, alumina called fumed alumina (typically, alumina fine particlesproduced when an alumina salt is fired at a high temperature) may beused based on the classification according to the production method.Further, alumina called colloidal alumina or alumina sol (for example,alumina hydrate such as boehmite) is also included in theabove-mentioned examples of known alumina. The alumina used as theabrasive grains of the polishing composition of the present inventionmay contain one kind of such alumina alone or in combination of two ormore kinds. Among these, alumina containing a γ phase (aluminacontaining γ-alumina) is preferable as a crystal phase, and aluminacontaining a γ phase (alumina containing γ-alumina as a main component)is more preferably as a main crystal phase.

In the present specification, in a case where the peak of the γ phaseappearing at a position of 2θ=46° is confirmed from the powder X-raydiffraction spectrum obtained by using the powder X-ray diffractometer,the alumina “contains the γ phase as the crystal phase”. Further, in thepresent specification, in a case where an austenitizing rate describedlater is more than 50%, it is determined that alumina “contains the γphase as the main crystal phase” (upper limit 100%). By using aluminacontaining a γ phase as the crystal phase, the polishing speed isfurther improved, and when the γ phase is the main crystal phase, theeffect is further enhanced. It is presumed that the γ phase has a largeamount of deformability when the stress is applied and contributes tothe improvement of the fracture strength. The alumina produced by thevaporized metal combustion method described later tends to have aparticularly high γ-phase content when a γ-phase peak appearing at theposition of 2θ=46° is confirmed.

In addition, a pregelatinization rate of alumina is preferably less than50%, more preferably less than 45%, and still more preferably less than40% (lower limit 0%). Within the above range, the polishing speed isfurther improved. It is presumed that although an α phase has highhardness, it tends to be brittle, and thus the fracture strength at thetime of applying the stress contributes to further improvement bykeeping the content below a certain level. Here, a pregelatinizationrate [%] can be calculated by the following equation, from a peak height(I25.6) of an α phase (012) plane appearing at the position of 2θ=25.6°and a peak height (I46) of a γ phase appearing at the position of 2θ=46°in a powder X-ray diffraction spectrum obtained by using a powder X-raydiffractometer.

Pregelatinization rate=I25.6/(I25.6+I46)×100 [unit: %]  [Equation 2]

In the case where the γ phase is contained as the main crystal phase, itis preferable to further contain the α phase as the crystal phase. Inthis case, the hardness is further improved and the polishing speed isfurther improved. At this time, the pregelatinization rate is preferablymore than 0% and less than 40%.

Further, in the present specification, the austenitizing rate [%] isdefined as a value calculated by the following equation, from a peakheight (I25.6) of an α phase (012) plane appearing at the position of2θ=25.6° and a peak height (I46) of a γ phase appearing at the positionof 2θ=46° in a powder X-ray diffraction spectrum obtained by using apowder X-ray diffractometer.

Austenitizing rate=I46/(I25.6+I46)×100 [unit: %]  [Equation 3]

The type of the crystal phase in alumina and the content ratio thereofcan be controlled by a production method and production conditions. Forexample, alumina produced by the vaporized metal combustion methoddescribed later has a higher austenitizing rate and a lowerpregelatinization rate. Further, in the vaporized metal combustionmethod, the pregelatinization rate can be lowered by lowering theheating temperature after the vaporized metal combustion reaction to1225° C.

Details of the identification of the type of the crystal phase inalumina, the measurement of the pregelatinization rate and theaustenitizing rate, the measurement of the calculation method, and thecalculation method will be described in examples.

In addition, the pregelatinization rate and the austenitizing ratecalculated based on the above measurement is the same value even if themeasurement is performed in a state where powdered alumina which is araw material of the polishing composition or alumina is taken out fromthe prepared polishing composition and measured.

The method for producing alumina used in the present invention is notparticularly limited, and a known method can be appropriately used.Among these, the method for producing alumina by the VMC method:vaporized metal combustion method is preferable because alumina havingan aspect ratio of 1.1 or less can be obtained. That is, the alumina ispreferably alumina produced by the vaporized metal combustion method. Byadopting the vaporized metal combustion method, alumina having an aspectratio of 1.1 or less can be obtained, and the polishing speed is furtherimproved by using the particles. Further, the alumina obtained by thevaporized metal combustion method has a high fracture strength (forexample, a fracture strength of 0.5 GPa or more). In the presentinvention, since the polishing speed is further improved by using theabrasive grains having high fracture strength, it is preferable toproduce alumina by the vaporized metal combustion method from theviewpoint of the fracture strength.

The vaporized metal combustion method means “a method of: forming achemical flame in an atmosphere containing oxygen; charging into thechemical flame such an amount of a metallic powder which constitutes apart of oxide particles of interest that a dust cloud is formed; andcausing deflagration to obtain the oxide particles.” Details of thevaporized metal combustion method are described in known documents suchas JP 60-255602 A, and alumina can be produced with reference to thesedescriptions. Further, in the vaporized metal combustion method, in thevaporized metal combustion reaction, the value of the fracture strengthcan be increased by pretreating the powder fluid of the metal alumina asthe pre-raw material at the heating temperature of more than 1200° C.Further, for ease of control, the heating temperature in the vaporizedmetal combustion reaction is preferably between 1250° C. and 1275° C. Inthe vaporized metal combustion method, the aspect ratio can beapproached to 1 by lowering the heating temperature after the vaporizedmetal combustion reaction below 1225° C. In the heat treatment, a knownapparatus/method such as a rotary kiln can be adopted.

A lower limit of the content (concentration) of the abrasive grains inthe polishing composition of the present invention is preferably 0.2% bymass or more, more preferably 0.3% by mass or more, and is still morepreferably 0.5% by mass or more, based on the polishing composition.Further, the upper limit of the content of the abrasive grains in thepolishing composition of the present invention is preferably 20% by massor less, more preferably 15% by mass or less, still more preferably 10%by mass or less, and even more preferably 5% by mass or less, based onthe polishing composition. Within such a range, the polishing speed canbe more improved. Note that, in a case where the polishing compositioncontains two or more types of abrasive grains, the content of theabrasive grains is intended to be the total amount of these.

[Basic Inorganic Compounds]

The polishing composition of the present invention contains a basicinorganic compound which is an alkali metal salt. Here, the basicinorganic compound refers to an inorganic compound having a function ofraising a pH of the composition by being added to the polishingcomposition. The basic inorganic compound has a function of chemicallypolishing the surface of the object to be polished and a function ofimproving the dispersion stability of the polishing composition.Further, the basic inorganic compound contained in the polishingcomposition of the present invention tends to increase the electricalconductivity of a polishing composition as compared with the basicorganic compound. It is considered that this further improves thepolishing speed by the polishing composition.

Further, the basic inorganic compound which is an alkali metal salt doesnot have a three-dimensional bulkiness as compared with the basicorganic compound, and thereby, the basic inorganic compound and theanionic water-soluble polymer are less likely to form an aggregate.Therefore, in the polishing composition of the present invention, sincethe anionic water-soluble polymer is in a stable dispersed state, theanionic water-soluble polymer can be efficiently adhered to thepolishing pad.

Examples of the basic inorganic compound which is an alkali metal saltinclude lithium hydroxide, lithium carbonate, potassium hydroxide,potassium carbonate, potassium hydrogen carbonate, tripotassiumphosphate, dipotassium hydrogen phosphate, sodium hydroxide, sodiumcarbonate, sodium hydrogen carbonate, trisodium phosphate, disodiumhydrogen phosphate, and the like. Among these, as the basic inorganiccompound of the alkali metal salt, potassium hydroxide and sodiumhydroxide are preferable, and potassium hydroxide is more preferable,from the viewpoint of pH and stability of the slurry.

In the embodiment of the present invention, the content of the basicinorganic compound in the polishing composition is preferably 0.001% bymass or more, more preferably 0.01% by mass or more, still morepreferably 0.05% by mass or more, and particularly preferably 0.1% bymass or more, based on the polishing composition. With such a lowerlimit, the polishing speed is further improved. The content of the basicinorganic compound in the polishing composition is preferably 10% bymass or more, more preferably 8% by mass or more, and still morepreferably 5% by mass or more, based on the polishing composition. Withsuch an upper limit, a stable slurry without agglomeration can beobtained.

[Anionic Water-Soluble Polymer]

The polishing composition of the present invention contains an anionicwater-soluble polymer. The anionic water-soluble polymer is awater-soluble polymer having an anionic group in the molecule. In thepresent specification, “water-soluble” means that the solubility inwater (25° C.) is 1 g/100 mL or more. The anionic water-soluble polymermay be used alone or in combination of two or more.

When the polishing composition of the present invention is used topolish the object to be polished, the anionic water-soluble polymercontained in the polishing composition adheres to a polishing pad. Atthis time, in a case where the zeta potential on the pad surface ispositive, the zeta potential becomes negative due to the adhesion of theanionic water-soluble polymer, and in a case where the zeta potential onthe pad surface is negative, the adhesion of anionic water-solublepolymer increases the absolute value of the zeta potential thereof. Forexample, when the polishing pad is polyurethane, the zeta potential onthe surface of the polyurethane is about −45 mV, but when the polishingpad comes into contact with the polishing composition of the presentinvention (that is, an anionic water-soluble polymer adheres), the zetapotential on the surface of the polishing pad can be increased to −80mV. Therefore, the anionic water-soluble polymer adheres to the surfaceof the polishing pad to make the surface charge of the polishing padnegative, or increasing the absolute value of the negative surfacecharge of the polishing pad guides the polishing pad and the abrasivegrains to repel more, which improves the polishing speed.

According to the embodiment of the present invention, as the anionicwater-soluble polymer, those containing at least one functional groupselected from the group consisting of a carboxyl group, a sulfo group, aphosphoric acid group, and a phosphonic acid group in the molecule arepreferable. Among them, the anionic water-soluble polymer preferablycontains a carboxyl group. By containing such a group in the anionicwater-soluble polymer, the desired effect of the present invention canbe efficiently exerted.

Further, according to the embodiment of the present invention, it ispreferable that the anionic water-soluble polymer has a constituent unitderived from a monomer having an ethylenically unsaturated bond. Forexample, the anionic water-soluble polymer preferably contains at leastone selected from the group consisting of acrylic acid and methacrylicacid as a constituent unit derived from the monomer. Therefore, it ismore preferable that the anionic water-soluble polymer is at least oneselected from the group consisting of a polyacrylic acid-based polymerand a polymethacrylic acid-based polymer. According to such anembodiment, it is presumed that a carboxyl group interacts with thebasic inorganic compound in the polishing composition, and the abrasivegrains are stably dispersed.

The anionic water-soluble polymer may be a copolymer containing aconstituent unit derived from a monomer having an ethylenicallyunsaturated bond in one molecule and a constituent unit derived fromanother monomer. Examples of such a copolymer include a copolymer of(meth)acrylic acid and vinyl alcohol, a copolymer of (meth)acrylic acidand 2-hydroxy-2-phosphonoacetic acid (HPAA), a copolymer of(meth)acrylic acid and acrylic morpholine (ACMO), and the like. Notethat, the term of (meth)acrylic acid comprehensively refers to acrylicacid and methacrylic acid.

Further, the anionic water-soluble polymer may contain an oxyalkyleneunit. Examples of the oxyalkylene unit that can be contained in theanionic water-soluble polymer include polyethylene oxide (PEO), a blockcopolymer of ethylene oxide (EO) and propylene oxide (PO), a randomcopolymer of EO and PO, and the like. The block copolymer of EO and POmay be a diblock body containing a polyethylene oxide (PEO) block and apolypropylene oxide (PPO) block, a triblock body, and the like. Thetriblock body includes a PEO-PPO-PEO type triblock body and aPPO-PEO-PPO type triblock body.

In the embodiment of the present invention, the lower limit of themolecular weight (mass average molecular weight) of the anionicwater-soluble polymer is preferably 1,000 or more, 5,000 or more, 10,000or more, 50,000 or more, 100,000 or more, 300,000 or more, 500,000 ormore, and 800,000 or more in this order. The upper limit of themolecular weight (mass average molecular weight) of the anionicwater-soluble polymer is preferably 8,500,000 or less, 6,000,000 orless, 4,000,000 or less, 2,000,000 or less, and 1,500,000 or less inthis order. That is, the molecular weight (mass average molecularweight) of the anionic water-soluble polymer is, for example, preferably1,000 or more and 8,500,000 or less, 5,000 or more and 6,000,000 orless, 10,000 or more and 4,000,000 or less, 50,000 or more and 4,000,000or less, and 100,000 or more and 2,000,000 or less in this order. Withinsuch a range, the polishing speed can be more improved. As the molecularweight (mass average molecular weight) of the anionic water-solublepolymer, a value measured by the GPC method can be adopted.

In the embodiment of the present invention, the content of the anionicwater-soluble polymer in the polishing composition is preferably 0.001%by mass or more, more preferably 0.005% by mass or more, still morepreferably 0.01% by mass or more, and even more preferably 0.05% by massor more, and most preferably 0.08% by mass or more, based on thepolishing composition In addition, the content of the anionicwater-soluble polymer in the polishing composition is 0.8% by mass orless, more preferably 0.5% by mass or less, and particularly preferably0.4% by mass, based on the polishing composition. Within such a range, ahigh polishing speed can be maintained. Note that, when the polishingcomposition contains two or more kinds of anionic water-solublepolymers, the content of the anionic water-soluble polymer means thetotal amount of them.

[Dispersing Medium]

The polishing composition contains a dispersing medium (solvent) fordispersion of each component constituting the polishing composition. Thedispersing medium has a function of dispersing or dissolving eachcomponent. Examples of the dispersing medium include an organic solventand water, and the dispersing medium preferably contains water, and ismore preferably water.

As the dispersing medium, water which does not contain impurities asmuch as possible is preferable from the viewpoint of suppressing thecontamination of the object to be polished and inhibition of the actionsof other components. As such water, for example, water having a totalcontent of transition metal ions of 100 ppb or less is preferable. Here,the purity of water can be increased by operations of removal ofimpurity ions using an ion exchange resin, removal of foreign mattersthrough a filter, distillation, and the like, for example. Specifically,as water, for example, deionized water (ion-exchanged water), purewater, ultrapure water, distilled water, or the like is preferably used.Usually, 90% by volume or more of the dispersing medium contained in thepolishing composition is preferably water, 95% by volume or more is morepreferably water, and 99% by volume or more is still more preferablywater, and 100% by volume is particularly preferably water.

Further, the dispersing medium may be a mixed solvent of water and anorganic solvent for dispersion or dissolution of each component. In thiscase, examples of the organic solvent to be used include acetone,acetonitrile, ethanol, methanol, isopropanol, glycerin, ethylene glycol,propylene glycol and the like, which are organic solvents that are mixedwith water. Alternatively, these organic solvents may be used withoutbeing mixed with water to disperse or dissolve each component and thenbe mixed with water. The organic solvents may be used either singly orin combination of two or more types.

[Other Additives]

The polishing composition of the present invention may further contain,as long as the effects of the present invention are not impaired, knownadditives such as a pH adjusting agent, a chelating agent, a thickener,an oxidizing agent, a dispersant, a surface protectant, a wetting agent,a surfactant, a rust preventive, an antiseptic agent, and an antifungalagent. The content of the additive may be appropriately set according tothe purpose of the addition.

(pH Adjusting Agent)

The polishing composition of the present invention can adjust the pHwithin a desired range with a basic inorganic compound, but may furthercontains a pH adjusting agent other than the basic inorganic compound.

As the pH adjusting agent, known acids, bases other than the basicinorganic compounds, or salts thereof can be used. Specific examples ofthe acid that can be used as the pH adjusting agent include inorganicacids such as hydrochloric acid, sulfuric acid, nitric acid,hydrofluoric acid, boric acid, carbonic acid, hypophosphite, phosphite,and phosphoric acid; and organic acids such as formic acid, acetic acid,propionic acid, butyric acid, valeric acid, 2-methyl butyric acid,n-hexanoic acid, 3,3-dimethyl butyric acid, 2-ethyl butyric acid,4-methyl pentanoic acid, n-heptanoic acid, 2-methyl hexanoic acid,n-octanoic acid, 2-ethyl hexanoic acid, benzoic acid, glycolic acid,salicylic acid, glyceric acid, oxalic acid, malonic acid, succinic acid,glutaric acid, adipic acid, pimelic acid, maleic acid, phthalic acid,malic acid, tartaric acid, citric acid, lactic acid, diglycolic acid,2-furandicarboxylic acid, 2,5-furandicarboxylic acid, 3-furancarboxylicacid, 2-tetrahydrofurancarboxylic acid, methoxyacetic acid,methoxyphenylacetic acid, and phenoxyacetic acid.

Examples of the base other than the basic inorganic compound that can beused as the pH adjusting agent include basic organic compounds such asaliphatic amines such as ethanolamine and2-amino-2-ethyl-1,3-propanediol, aromatic amines, and tetraammoniumhydroxide, for example. Ammonia can also be used as a pH adjustingagent.

The pH adjusting agents may be used either singly or in combination oftwo or more types. The addition amount of the pH adjusting agent is notparticularly limited, and may be appropriately adjusted so that thepolishing composition is within a desired range.

The lower limit of the pH of the polishing composition is notparticularly limited, and is preferably 9.5 or more, more preferably 10or more, still more preferably 10.5 or more, and particularly preferably11 or more. With such a lower limit, the polishing speed of the objectto be polished can be improved. Further, the upper limit of the pH isnot particularly limited, but is preferably 13 or lower, more preferably12.5 or lower, and still more preferably 12 or lower. With such a lowerlimit, the stability of the polishing composition can be improved.

Note that, the pH of the polishing composition can be measured by, forexample, a pH meter.

<Method for Producing Polishing Composition>

The method for producing the polishing composition of the presentinvention is not particularly limited, and for example, the polishingcomposition can be obtained by stirring and mixing abrasive grains, abasic inorganic compound, an anionic water-soluble polymer, and ifnecessary, other additives in a dispersing medium. The details of eachcomponent are as described above. Therefore, the present inventionprovides a method for producing a polishing composition, which includesmixing abrasive grains, a basic inorganic compound, an anionicwater-soluble polymer, and a dispersing medium.

The temperature at which each component is mixed is not particularlylimited, and is preferably 10° C. or more and 40° C. or less, andheating may be performed to increase a rate of dissolution. In addition,a mixing time is also not particularly limited as long as uniform mixingis possible.

<Polishing Method and Producing Method of Semiconductor Substrate>

The present invention provides a polishing method including a step ofpolishing an object to be polished using the polishing compositionaccording to the embodiment of the present invention. The presentinvention also provides a method for producing a semiconductorsubstrate, which includes the above polishing method.

As a polishing apparatus, it is possible to use a general polishingapparatus to which a holder for holding a substrate or the like havingan object to be polished and a motor or the like capable of changing therotation speed are attached, and which includes a platen to which apolishing pad (polishing cloth) can be attached.

As the polishing pad, general non-woven fabric, polyurethane, porousfluororesin and the like can be used without particular limitation. Itis preferable that the polishing pad is subjected to groove processingso that a polishing solution is accumulated.

Regarding the polishing conditions, for example, the rotation speed ofthe platen is preferably 10 rpm (0.17 s⁻¹) or more and 500 rpm (8.3 s⁻¹)or less. The pressure (polishing pressure) applied to the substratehaving the object to be polished is preferably 0.5 psi (3.4 kPa) or moreand 10 psi (68.9 kPa) or less. The method for supplying the polishingcomposition to the polishing pad is not particularly limited, and forexample, a method for continuously supplying the composition with a pumpor the like is employed. The amount supplied is not particularlylimited, the surface of the polishing pad is preferably covered with thepolishing composition of the present invention all the time.

After completion of the polishing, the substrate is washed in flowingwater, and water droplets adhering to the substrate are removed by aspin dryer or the like to dry the substrate, thereby obtaining asubstrate having a metal-containing layer.

The polishing composition of the present invention may be aone-component type or a multi-component type including a two-componenttype. In addition, the polishing composition of the present inventionmay be prepared by diluting, for example, 10 times or more of the stocksolution of the polishing composition with a diluent such as water.

Although the embodiments of the present invention have been described indetail, note that this is illustrative and exemplary, and not limiting,and the scope of the present invention is to be interpreted by theappended claims.

The present invention includes the following aspects and embodiments.

1. A polishing composition containing abrasive grains; a basic inorganiccompound; an anionic water-soluble polymer; and a dispersing medium,

wherein a zeta potential of the abrasive grains is negative,

an aspect ratio of the abrasive grains is 1.1 or less,

in a particle size distribution of the abrasive grains obtained by alaser diffraction/scattering method, a ratio D90/D50 of a particlediameter D90 when an integrated particle mass reaches 90% of a totalparticle mass from a fine particle side to a particle diameter D50 whenthe integrated particle mass reaches 50% of the total particle mass fromthe fine particle side is more than 1.3, and

the basic inorganic compound is an alkali metal salt.

2. The polishing composition according to 1. above, wherein the anionicwater-soluble polymer is at least one selected from the group consistingof a polyacrylic acid-based polymer and a polymethacrylic acid-basedpolymer.

3. The polishing composition according to 1. or 2. above, wherein amolecular weight of the anionic water-soluble polymer is 5,000 or moreand 6,000,000 or less.

4. The polishing composition according to any one of 1. to 3. above,which a pH is 9.5 or higher.

5. The polishing composition according to any one of 1. to 4. above,wherein the abrasive grains contain alumina.

6. The polishing composition according to 5. above, wherein the aluminacontains a γ phase as a crystal phase.

7. The polishing composition according to 5. or 6. above, wherein apregelatinization rate of the alumina is less than 50%.

8. The polishing composition according to any one of 5. to 7. above,wherein a fracture strength of the alumina is 0.5 GPa or more.

9. A polishing method including polishing an object to be polished usingthe polishing composition according to any one of 1. to 8. above.

10. A method for producing a semiconductor substrate, which includes thepolishing method according to 9. above.

EXAMPLES

The present invention will be further described in detail using thefollowing examples and comparative examples. Here, the technical scopeof the present invention is not limited to the following examples. Inaddition, unless otherwise specified, “%” and “parts” mean “% by mass”and “parts by mass”, respectively. Further, in the following examples,unless otherwise specified, the operation was performed under theconditions of room temperature (20° C. to 25° C.)/relative humidity 40%RH to 50% RH.

[Preparation of Abrasive Grains]

(Alumina by Vaporized Metal Combustion Method: Production of AbrasiveGrains A)

Abrasive grains A were prepared by a vaporized metal combustion methodwith reference to the examples of JP 60-255602 A. Note that, in thefollowing description, the abrasive grains A produced by the vaporizedmetal combustion method may be referred to as “VMC alumina”. Thephysical properties of the obtained abrasive grains A (VMC alumina) werecalculated according to the following measurement method and are shownin Table 1 below.

(Sintered and Crushed α-Alumina: Production of Abrasive Grains B)

Sintered pulverized α-alumina was prepared as abrasive grains B.Specifically, as described in paragraph “0013” of JP 2006-36864 A, afterperforming calcination under the conditions in which the calcinationtemperature of aluminum hydroxide was in a range of 1100° C. to 1500°C., and the calcination time was in a range of 1 to 5 hours, theresultant was pulverized using an aluminum oxide pole having a diameterof 20,000 μm. Powdery sintered pulverized α-alumina was produced as theabrasive grains B by a method for producing alumina (crushing method) bycalcining in this way and then pulverizing if necessary. In theproduction of the abrasive grains B, the crushing time was controlled sothat the average particle size values indicated in Table below were ableto be obtained. The physical properties of the obtained abrasive grainsB (sintered pulverized α-alumina) were calculated according to thefollowing measurement method and are shown in Table 1 below.

[Analysis of Type and Content of Crystal Phase]

(Type of Crystal Phase Contained in Alumina)

Regarding the powdered abrasive grains (alumina), a powder X-raydiffraction spectrum was obtained using a powder X-ray diffractometer(fully automatic multipurpose X-ray diffractometer SmartLab manufacturedby Rigaku Corporation), and the type of crystal phase contained inalumina was determined from the peak position of the powder X-raydiffraction spectrum. In the present specification, in a case where thepeak of the α phase (012) plane appearing at a position of 2θ=25.6° wasconfirmed in the powder X-ray diffraction spectrum, it was determinedthat the alumina “contains the α phase as the crystal phase”. Inaddition, the peak of the γ phase appearing at a position of 2θ=46° wasconfirmed, it was determined that the alumina “contains the γ phase asthe crystal phase”.

(Pregelatinization Rate)

The pregelatinization rate [%] can be calculated by the followingequation, from a peak height (I25.6) of an a phase (012) plane appearingat the position of 2θ=25.6° and a peak height (I46) of a γ phaseappearing at the position of 2θ=46° in a powder X-ray diffractionspectrum obtained by using a powder X-ray diffractometer.

Pregelatinization rate=I25.6/(I25.6+I46)×100 [unit: %]  [Equation 4]

(Main Crystal Phase)

In a case where the pregelatinization rate was more than 50%, it wasdetermined that alumina particles “contain the α phase as the maincrystal phase”. Further, a value calculated by the following equation,from a peak height (I25.6) of an α phase (012) plane appearing at theposition of 2θ=25.6° and a peak height (I46) of a γ phase appearing atthe position of 2θ=46° in a powder X-ray diffraction spectrum obtainedby using a powder X-ray diffractometer, is defined as the austenitizingrate [%]. In a case where the austenitizing rate was more than 50%, itwas determined that alumina particles “contain the γ phase as the maincrystal phase”.

Austenitizing rate=I46/(I25.6+I46)×100 [unit: %]  [Equation 5]

[Aspect Ratio]

For powdered abrasive grains (alumina), the aspect ratio was calculatedby randomly selecting 100 abrasive grains from the images measured by ascanning electron microscope (SEM) (product name: SU8000 manufactured byHitachi High-Technology Co., Ltd.) and measuring and calculating theiraverage major axis and average minor axis. Subsequently, the aspectratio of the abrasive grains was calculated according to the followingequation using the values of the average major axis and the averageminor axis.

Aspect ratio=average major axis [μm]/average minor axis [μm]  [Equation6]

[Average Secondary Particle Size]

The powdered abrasive grains (alumina) were measured using a particlesize distribution measuring apparatus (MicrotracBEL Corp., MicrotracMT3000II), and the average secondary particle size was evaluated.

[Fracture Strength]

For the powdered abrasive grains (alumina), a load-push displacementdiagram was obtained by the following measuring apparatus and under thefollowing measuring conditions. Then, the fracture strength of theabrasive grains was calculated according to the following equation,assuming that the point where the displacement increases rapidly is apoint where large-scale fracture occurs in the particles.

S _(t)=(2.8×P)/(π×d ²)  [Equation 7]

in the equation,S_(t) represents a fracture strength [GPa],P represents a fracture load [kgf], andd represents an average particle size [μm] of particles.

(Measuring Apparatus and Measuring Conditions)

Measuring apparatus: Microcompression tester MCTW-500 manufactured byShimadzu Corporation,

Indenter used: Diamond flat indenter (φ=50 μm),

Load speed: 7.747 mN/s: Constant load speed method, and

Measurement atmosphere: Room temperature in the atmosphere.

Table 1 indicates the characteristics (material and producing method) ofeach abrasive grain and the evaluation results of a pregelatinizationrate, a main crystal phase, an average particle size, an aspect ratio,an average major axis, an average minor axis, and a fracture strength.

Note that, in Table 1 below, the pregelatinization rate of <40 [%] meansthat although the α phase is included as the crystal phase, the value ofthe pregelatinization rate is more than 0% and less than 40%, and thepregelatinization rate of >70 [%] means that an a phase is included asthe crystal phase, and the value of the pregelatinization rate is morethan 70%.

TABLE 1 Average Pregelatinization Main secondary Average AverageFracture Abrasive Production rate crystal particle size Aspect majoraxis minor axis strength grain method [%] phase [μm] ratio [μm] [μm][GPa] A (Alumina) Vaporized metal <40 γ 0.2 1.01 0.201 0.2 0.78combustion method (VMC) B (Alumina) Sintering- >70 α 1.3 1.6 1 0.6200.42 crushing method

[Preparation of Polishing Composition]

Example 1

Abrasive grains A (average primary particle size of 100 nm, averagesecondary particle size of 200 nm, and average association degree 2)obtained above as abrasive grains, polyacrylic acid (PAA) with amolecular weight (mass average molecular weight) of 1,000,000 as awater-soluble polymer, and potassium hydroxide as a basic compound andion-exchanged water were stirred and mixed to reach the finalconcentration thereof, 1.0% by mass, 0.1% by mass, and 0.2% by mass,respectively, at room temperature (25° C.) for 30 minutes to prepare apolishing composition. A pH of the polishing composition measured by apH meter (HORIBA, Ltd. Model No.: LAQUA (registered trademark)) was12.0. Note that, the zeta potential of the abrasive grains A in theobtained polishing composition was −30 mV as measured by the followingmethod. Table 2 indicates the results of the average primary particlesize, the average secondary particle size, D90/D50, and the aspect ratiomeasured by the above method for the abrasive grains A in the obtainedpolishing composition.

Note that, the particle size of the abrasive grain A in the polishingcomposition was the same as the particle size of the powdered alumina inTable 1 above.

Therefore, although powdered alumina was used as the measurement samplefor the aspect ratio, the abrasive grains A in the polishing compositionmay be taken out and measured in the same manner.

In addition, “broad” in the particle size distribution column in Table 2means that D90/D50 is more than 1.3, and “sharp” means that D90/D50 is1.3 or less. Further, “spherical” in the particle shape column in Table2 means that the aspect ratio is 1.1 or less, and “variant” means thatthe aspect ratio is more than 1.1. In Table 3, “PAA” representspolyacrylic acid, and “-” represents that the component is notcontained.

Example 2 and Comparative Examples 1 to 3

The polishing compositions according to Example 2 and ComparativeExamples 1 to 3 were prepared in the same manner as in Example 1 exceptthat the type of the water-soluble polymer and the type of the basiccompound were changed as indicated in Table 3 by using the abrasivegrains shown in Table 2. Table 2 indicates the results of the zetapotential, the average primary particle size, the average secondaryparticle size, D90/D50, and the aspect ratio measured by the abovemethod for the abrasive grains A in the obtained polishing composition.Note that, the particle size of the abrasive grain in the polishingcomposition was the same as the particle size of the powdered alumina inTable 1 above. The pH of the obtained polishing composition is indicatedin Table 3 below.

EVALUATION

[Zeta Potential Measurement]

Each polishing composition prepared below was put in ELS-Z2 manufacturedby Otsuka Electronics Co., Ltd., to perform a measurement at temperature25° C. using a flow cell by a laser Doppler method (electrophoreticlight scattering measurement method). The zeta potential of the aluminain the polishing composition was calculated by analyzing the obtaineddata by the Smoluchowski equation.

[Measurement of Average Primary Particle Size]

The average primary particle size of the abrasive grains was calculatedfrom the specific surface area of the abrasive grains measured by a BETmethod using “Flow SorbII 2300” manufactured by Micromeritics and thedensity of the abrasive grains. Further, the average secondary particlesize of the abrasive grains was measured by a dynamic light scatteringparticle diameter and particle size distribution device UPA-UTI 151manufactured by Nikkiso Co., Ltd.

[Measurement of Average Secondary Particle Size]

The average secondary particle size of the abrasive grains was measuredby a light scattering method using a laser beam, and Microtrac MT3000II(manufactured by MicrotracBEL Corp) was used as a measuring machine.Note that, in the particle size distribution of the average secondaryparticle size of the abrasive grains, a ratio D90/D50 of a particlediameter D90 when an integrated particle mass reached 90% of a totalparticle mass from the fine particle side to a particle diameter D50when the integrated particle mass reached 50% of the total particle massfrom the fine particle side was calculated.

[Polishing Speed]

As an object to be polished, a silicon wafer (200 mm, blanket wafer,manufactured by Advantec Co., Ltd.) having a TEOS film with a thicknessof 10000 Å on the surface and a silicon wafer (200 mm, blanket wafer,manufactured by Advantec Co., Ltd.) having a SiN film with a thicknessof 3500 Å on the surface. A coupon obtained by cutting each siliconwafer into chips of 60 mm×60 mm was used as a test piece, and thesubstrate was polished under the following polishing conditions usingeach of the polishing compositions obtained above. The two types ofobjects to be polished were polished under the following conditions.Note that, the polishing speed of the SiN film was measured only in thepolishing compositions of Example 1 and Comparative Example 1.

(Polishing Conditions)

⋅ TEOS Film

EJ-380IN-CH (manufactured by Engis Japan Corporation) was used as apolishing machine, and rigid polyurethane pad IC1000 (manufactured byRohm and Haas Company) was used as a polishing pad. Polishing wascarried out with a polishing time of 60 seconds under the conditions ofa polishing pressure of 3.05 psi (21.0 kPa), a platen rotation speed of60 rpm, a carrier rotation speed of 60 rpm, and a supply rate of thepolishing composition of 100 ml/min.

⋅ SiN Film

EJ-380IN-CH (manufactured by Engis Japan Corporation) was used as apolishing machine, and rigid polyurethane pad IC1000 (manufactured byRohm and Haas Company) was used as a polishing pad. Polishing wascarried out with a polishing time of 60 seconds under the conditions ofa polishing pressure of 4.0 psi (27.6 kPa), a platen rotation speed of113 rpm, a carrier rotation speed of 107 rpm, and a supply rate of thepolishing composition of 200 ml/min.

(Polishing Speed)

The polishing speed (Removal Rate; RR) was calculated by the followingequation. Note that, 1 Å=0.1 nm is established.

$\begin{matrix}{{{Polishing}\mspace{14mu}{{speed}\mspace{14mu}\left\lbrack {\mathring{\mathrm{A}}/\min} \right\rbrack}} = \frac{\begin{matrix}{{{film}\mspace{14mu}{thickness}\mspace{14mu}{before}\mspace{14mu}{{polishing}\mspace{14mu}\lbrack\mathring{\mathrm{A}}\rbrack}} -} \\{{film}\mspace{14mu}{thickness}\mspace{14mu}{after}\mspace{14mu}{{polishing}\mspace{14mu}\lbrack\mathring{\mathrm{A}}\rbrack}}\end{matrix}}{{polishing}\mspace{14mu}{{time}\mspace{14mu}\left\lbrack \min \right\rbrack}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

The film thickness was determined by light interference type filmthickness measurement apparatus (Model No.: Lambda Ace VM-2030,manufactured by Dainippon Screen Mfg. Co., Ltd.), and the polishingspeed was evaluated by dividing the difference between film thicknessbefore and film thickness after polishing by the polishing time.

The evaluation results of the polishing speed for the TEOS film areindicated in Table 3 below.

The polishing speed for the SiN film was 376 Å/min when the polishingcomposition of Example 1 was used, and was 260 Å/min when the polishingcomposition of Comparative Example 1 was used.

[Number of Scratches]

An object to be polished to be evaluated for the number of scratches wasprepared. First, as an object to be polished, a silicon wafer (200 mm,blanket wafer, manufactured by Advantec Co., Ltd.) having a TEOS filmwith a thickness of 10000 Å on the surface and a silicon wafer (200 mm,blanket wafer, manufactured by Advantec Co., Ltd.) having a SiN filmwith a thickness of 3500 Å on the surface. These two types of objects tobe polished were polished under the following polishing conditions usingthe polishing compositions of Example 1 and Comparative Example 4obtained above.

(Polishing Conditions for Evaluating the Number of Scratches)

Polishing apparatus: CMP single-sided polishing apparatus for 200 mmMirra, manufactured by Applied Materials, Inc.

Pad: Nitta Haas Incorporated, Hard polyurethane pad IC1010

Polishing pressure: 2.0 psi

Platen rotation speed: 83 rpm

Carrier rotation speed: 77 rpm

Supply of polishing composition: Flowing

Supply amount of polishing composition: 200 ml/min

Polishing time: 60 sec

The number of scratches on the surface of the object to be polishedafter polishing was measured by measuring the coordinates of the entiresurface (excluding the outer circumference of 2 mm) of both sides of theobject to be polished using the wafer inspection apparatus “Surf scan(registered trademark) SP2” manufactured by KLA-Tencor Corporation, andthen, observing all the measured coordinates with Review-SEM (RS-6000,manufactured by Hitachi High-Tech Corporation). Note that, the scratcheson the surface of the substrate having a depth of 10 nm or more and lessthan 100 nm, a width of 5 nm or more and less than 500 nm, and a lengthof 100 μm or more were counted as scratches, and scratch evaluation wasperformed according to the following criteria.

[Scratch Evaluation Criteria]

∘ . . . The number of scratches is less than 10, which is good.

x . . . The number of scratches is 10 or more, which is defective.

As a result of counting the scratches, when the polishing composition ofExample 1 was used, the scratch evaluation was ∘, and when the polishingcomposition of Comparative Example 3 was used, the scratch evaluationwas x.

TABLE 2 Abrasive grain Average Average Zeta primary secondary ParticleAbrasive Production potential particle particle size Particle Aspectgrain method (mV) (nm) (nm) D90/D50 distribution shape ratio Example 1 AVMC Alumina −30 mV 100 200 2.8 Broad Spherical 1.01 Example 2 A VMCAlumina −30 mV 100 200 2.8 Broad Spherical 1.01 Comparative A VMCAlumina −30 mV 100 200 2.8 Broad Spherical 1.01 Example 1 Comparative AVMC Alumina −30 mV 100 200 2.8 Broad Spherical 1.01 Example 2Comparative B Sintered crushed −30 mV 700 1280 2.8 Broad Variant 1.60Example 3 α-alumina

TABLE 3 TEOS Abrasive grain Basic compound Water-soluble polymerpolishing Content Concentration Molecular Concentration speed Types (%by mass) Types [mass %] Types weight [mass %] pH (Å/min) Example 1 A 1.0KOH 0.2 PAA 1000000 0.1 12 745 Example 2 A 1.0 KOH 0.2 PAA 100000 0.1 12500 Comparative A 1.0 KOH 0.2 — — — 12 436 Example 1 Comparative A 1.0Ammonia 0.2 PAA 1000000 0.1 12 24 Example 2 Comparative B 1.0 KOH 0.2PAA 1000000 0.1 12 650 Example 3

As indicated in Table 3, it was found that in a case where the polishingcompositions of Examples 1 and 2 were used, the polishing speed withrespect to the TEOS film exceeded 450 Å/min, and the TEOS film was ableto be polished at a high polishing speed as compared with the polishingcompositions of Comparative Examples 1 and 2.

Further, it was found that the polishing composition of ComparativeExample 3 had a high polishing speed with respect to the TEOS film, butscratches were easily formed. The reason for this is presumed that thescratches are more likely to be formed as a result of the suppression ofrolling of irregularly shaped particles having an aspect ratio of morethan 1.3 by the abrasive grains.

On the other hand, in the polishing composition of Example 1, thescratches are suppressed as compared with the polishing composition ofComparative Example 3. It is considered that this is a result of thecharacteristics such as the aspect ratio, particle size, particle sizedistribution, and hardness of the abrasive grains A used in thepolishing composition of Example 1 acting on the polishing speed in awell-balanced manner.

Comparing Example 1 with Comparative Example 3, when the basic inorganiccompound contained in the polishing composition is not an alkali metalsalt, the polishing speed by the polishing composition is significantlyreduced.

From this, it can be seen that the polishing speed of the object to bepolished is improved when the polishing composition contains the basicinorganic compound which is an alkali metal salt and the anionicwater-soluble polymer.

This application is based on Japanese Patent Application No. 2020-049621filed on Mar. 19, 2020, the disclosure of which is incorporated hereinby reference in entirety thereof.

What is claimed is:
 1. A polishing composition comprising: abrasivegrains; a basic inorganic compound; an anionic water-soluble polymer;and a dispersing medium, wherein a zeta potential of the abrasive grainsis negative, an aspect ratio of the abrasive grains is 1.1 or less, in aparticle size distribution of the abrasive grains obtained by a laserdiffraction/scattering method, a ratio D90/D50 of a particle diameterD90 when an integrated particle mass reaches 90% of a total particlemass from a fine particle side to a particle diameter D50 when theintegrated particle mass reaches 50% of the total particle mass from thefine particle side is more than 1.3, and the basic inorganic compound isan alkali metal salt.
 2. The polishing composition according to claim 1,wherein the anionic water-soluble polymer is at least one selected fromthe group consisting of a polyacrylic acid-based polymer and apolymethacrylic acid-based polymer.
 3. The polishing compositionaccording to claim 1, wherein a molecular weight of the anionicwater-soluble polymer is 5,000 or more and 6,000,000 or less.
 4. Thepolishing composition according to claim 1, wherein a pH is 9.5 orhigher.
 5. The polishing composition according to claim 1, wherein theabrasive grains contain alumina.
 6. The polishing composition accordingto claim 5, wherein the alumina contains a γ phase as a crystal phase.7. The polishing composition according to claim 5, wherein apregelatinization rate of the alumina is less than 50%.
 8. The polishingcomposition according to claim 5, wherein a fracture strength of thealumina is 0.5 GPa or more.
 9. A polishing method comprising: polishingan object to be polished using the polishing composition according toclaim
 1. 10. A method for producing a semiconductor substrate,comprising: the polishing method according to claim 9.